The present invention relates to a suede-like sheet and to its method of production. More particularly, it relates to a suede-like sheet which is outstanding in its handle, strength, product quality and durability, and to a method for the production thereof.
Suede-like sheet obtained by impregnating a sheet-shaped material comprising synthetic fibre with a polymer elastomer has an evenness, dye fastness and softness of handle not to be found with natural leather, and it has been widely used in clothing, furnishings and seating applications. In particular, suede-like sheet comprising primarily ultrafine fibre of fineness no more than 0.3 dtex and a polyurethane is outstanding in its product quality, surface feel and handle, and is widely employed not only for clothing but also for upholstery, car seats and the like.
However, when such suede-like sheet is used over a prolonged period, problems can arise such as rupture, or the nap being locally extended and entangled so that so-called fraying and pilling occur. One of the causes of such problems is degradation of the polyurethane and a number of attempts have been made to overcome this by employing a highly durable polyurethane.
For example, in terms of hydrolysis resistance, polyurethane employing a polyether-type diol (hereinafter referred to as a polyether-based polyurethane) is outstanding, but it has the problem of poor light resistance. On the other hand, polyurethane employing a polyester diol (hereinafter referred to as a xe2x80x9ca polyester-based polyurethanexe2x80x9d) is excellent in its light resistance but it has poor hydrolysis resistance. Again, polyurethane employing a polycarbonate diol (hereinafter referred to as xe2x80x9ca polycarbonate-based polyurethanexe2x80x9d) has comparatively good light resistance and hydrolysis resistance, but it is physically hard and there are difficulties in obtaining products with a soft handle. To overcome the disadvantages of the polycarbonate-based polyurethane, there have been proposed polyurethanes employing polycarbonate diols of special structure, and artificial leathers employing these polyurethanes have been proposed.
For example, in JP-A-5-43647, there is a description to the effect that by using a polyurethane which employs a non-crystalline polycarbonate diol there is obtained a leather-like sheet which is outstanding in its wear resistance, softness and hydrolysis resistance, but even using a polyurethane employing such a non-crystalline polycarbonate there is in fact very little improvement in the softness and this remains a long way from target levels.
Furthermore, in JP-A-4-300368 there is described the use of a polyurethane which includes a polyester-based diol containing dicarboxylic acid units and C5-C6 alkanediol units derived from optionally methyl-substantially comprising carbanyl units and C8 to C10 alkanediol units derived from at least one type of alkanediol selected from the group comprising optionally methyl-substituted 1,8-octanediol and 1,9-nonanediol. In this way, an artificial leather is obtained which combines both softness and durability but, even by this method, there is not obtained leather-like sheet having sufficient durability.
Moreover, if one attempts to soften the sheet-shaped material with a reduction in the amount of polyurethane applied, when the sheet is used for a prolonged period degradation of the polyurethane remains unavoidable and adequate durability is not obtained. In particular, the local failure resistance is unsatisfactory.
If an attempt is made to obtain a soft leather-like sheet suitable for light garments in particular, it becomes even more difficult to achieve a good balance of softness and durability, and in practice it is currently impossible to obtain a sheet where these are satisfactory.
Thus, as explained above, hitherto, merely by improving polyurethane durability, it has not been possible to obtain a suede-like sheet, in particular a thin suede-like sheet, which is outstanding in its softness, strength and durability.
The first objective of the present invention lies in providing a suede-like sheet which combines softness, good handle and elegant appearance, and which is outstanding in its durability (specifically in its local failure resistance, fraying resistance and pilling resistance).
The suede-like sheet of the present invention which achieves this objective has the following constitution. Specifically, it is a suede-like sheet which is characterized in that, in a suede-like sheet comprising primarily ultrafine fibre of no more than 0.3 dtex and polyurethane, said polyurethane employs polymer diol containing 30 wt % to 90 wt % polycarbonate diol, said sheet contains 20 wt % to 60 wt % of said polyurethane, the average nap length is 300 xcexcm to 2000 xcexcm, and the percentage retention of the local failure resistance before and after an accelerated aging treatment is at least 50%.
An objective of the invention also lies in providing a method for stably producing this suede-like sheet. For this, the invention has the following constitution.
Specifically, it is a method for the production of a suede-like sheet which is characterized in that, in the preparation of a suede-like sheet comprising a nonwoven fabric of ultrafine fibre of no more than 0.3 dtex and a polyurethane employing polymer diol containing 30 wt % to 90 wt % polycarbonate diol, a buffing treatment is carried out after applying an antistatic agent to the sheet.